The present invention relates to a brush holder assembly for conducting electrical current between a brush and a rotating element of a dynamoelectric machine. In particular, the brush holder assembly can be replaced during operation of the machine.
A dynamoelectric machine has a rotor with windings that conduct electrical current for operation of the machine. Because the rotor rotates, rotating elements are used to conduct current to the rotor windings from a source external to the rotor. The rotating elements such as collector rings or commutators make contact with brushes to conduct the current. As the brushes are stationary with respect to the rotating elements, the brushes, which are made of carbon, wear due to friction and need periodic replacement.
Commercial electric generators are expensive to operate and need to generate revenue to support operations. Hence, a major goal in operating the generator is to reduce downtime for maintenance. To this end, the brushes are designed to be replaced while the generator is operating. As the generator is operating during brush replacement, safety is of the utmost concern.
In order to safely change the brushes, an operator uses only one hand. Using two hands increases the probability of an accident with current flowing from one hand to another hand through the operator's body. Even with appropriate protective personnel equipment, using only one hand is very important to reduce the risk of serious injury.
Older brush holder designs for replacing the brushes while the generator is operating have some drawbacks. For example, one type of brush holder weighs about ten pounds making it difficult for the operator to change out using only one hand. There are both ergonomic and safety concerns with this design. Also, while the brush surfaces are exposed to cooling air, it is difficult to see the amount of brush wear in order to determine an appropriate time for brush replacement.
As another example, other brush holders are somewhat lighter at five pounds but still too heavy to be conveniently changed out with only one hand. These brush holders are generally complicated and expensive. In addition, these brush holders use a box-style enclosure around each brush. Unfortunately, the box-style enclosure limits the amount of brush surface exposed to cooling air, thus, shortening the life span of the brush.
Some of the brush holders with the box-style enclosures hold only a single brush, which means the operator must reach into the energized brush-rigging/collector assembly for brush changing twice as many times as a two-brush holder design. In addition, it is difficult to see the amount of brush wear using the box-style enclosure design. One box-style holder design uses a wear indicator attached to each individual brush, increasing the cost of each brush and, therefore, maintenance costs.
Therefore, what are needed are techniques that allow changing brushes in a dynamoelectric machine safely, quickly, and inexpensively. In particular, the brush changing needs to be performed while the machine is operational.